A way to erase OTP components?

From: Don Maslin <donm_at_cts.com>
Date: Wed Jan 22 23:26:00 2003

On Wed, 22 Jan 2003, Bob Shannon wrote:

> I currently work for a company that makes the X-Ray supplies for airport
> scanners. We have the full X-Ray
> emitter heads at test loads for the -180KV, 15ma supplies in-house.
>
> These scanners place the high voltage under computer control, they don't
> run at any one preset level. I gather
> that the operating point shifts as the tubes age, and perhaps also with
> the material being examined under software
> control.
>
> But crank one of these babies up to full power, and the X-rays will
> generate very high charge levels in the die and
> cook the part.
>
> The question now becomes, does the date go away before the transistors do?
>
> On a related note, I recently erased a (windowed) 27C512 using a UV led.
> I did'nt think it would work, but it did.

How long did it take?
                                                - don

> Eric Smith wrote:
>
> >Bob Shannon wrote:
> >
> >>X-rays will erase the part at high energy levels, but this will also
> >>degrade the part to the point where it
> >>will fail soon, or die during erasure.
> >>
> >
> >A friend had a large quantity of programmed 27C512 OTP EPROMs, with
> >contents of no use to him. He tried to erase them using a commerical
> >X-ray machine, of the type used for inspecting assembled circuit boards
> >(to check solder joints on BGA packages) and was unable to produce any
> >noticable change to the part.
> >
> >This subject has been discussed on sci.electronics multiple times in the
> >past, and the consensus was that the frequency of Xrays is such that
> >they have no direct effect on the stored data. But at very high
> >exposures it is definitely possible to damage the part.
> >
> >Note that the exposure levels used for baggage inspection at airports
> >is far too low to cause any measurable effect on EPROMs. They are
> >generally set to substantially lower levels than medical X-rays
> >equipment.
> >
> >The normal erasure procedure for EPROMs is to use short-wave UV light,
> >nominally at a wavelength of 2537 angstroms (about 254 nm). Unlike the
> >more common long-wave UV (black lights), this *is* dangerous to your eyes;
> >never look into the light. The light bulbs and the window on the EPROM
> >are made from quartz rather than glass, because glass blocks most of the
> >short-wave UV. Suitable bulbs are commonly sold for germicidal use.
> >
> >In the mid-1980s, at least one Japanese semiconductor company offered
> >plastic windowed EPROMs. The package was a normal epoxy DIP package,
> >except that a square area in the center was molded from a different
> >plastic. The window was translucent (not transparent) to visible light.
> >These were less expensive than the usual ceramic windowed parts, but
> >more expensive than OTP parts. However, they could only be erased a
> >small number of times because the plastic window becomes opaque to the
> >shortwave UV with prolonged exposure.
> >
> >I'd heard of these plastic windowed packages at the time, but never
> >actually saw one until I purchased a coin-op video game board at an
> >auction.
> >
> >Eric
> >
> >
> >
> >
> >
>
>
>
Received on Wed Jan 22 2003 - 23:26:00 GMT